Methods for monitoring antigen-specific immune responses are important for evaluating the efficacy of immunotherapies such as cancer vaccines. Detection of tumor-specific immune responses can be particularly difficult because tumor antigens are typically self-antigens which are poorly immunogenic. Also, assays in which cell-mediated immune responses are detected in vitro require the use of antigen presenting cells (APC) that are immunologically compatible with the test cells. In other words, in vitro assays to detect antigen-dependent activation of lymphocytes such as T cells employ APC (i) that display major histocompatibility complex antigens (MHC) recognized by antigen receptors expressed on the lymphocyte and (ii) that do not elicit non-specific responses from the lymphocytes.